This disclosure includes a microfiche appendix of 1,150 frames on 12 fiches, the entirety of which is copyright(copyright) 1993, 1994, Coltec Industries, Inc. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
This invention relates to electronic control systems and control methods for operating one or more compressors, particularly including rotary screw compressors.
Rotary screw compressors, such as the compressor disclosed in U.S. Pat. No. 4,435,139, have long been used to provide compressed air in industry. The rotary screw compressor comprises two rotors mounted in a working space limited by two end walls and a barrel wall extending therebetween. The barrel wall takes the shape of two intersecting cylinders, each housing one of the rotors. Each rotor is provided with helically extending lobes and grooves which are intermeshed to establish chevron shaped compression chambers. In these chambers, a gaseous fluid is displaced and compressed from an inlet channel to an outlet channel by way of the screw compressor. Each compression chamber during a filling phase communicates with the inlet, during a compression phase undergoes a continued reduction in volume, and during a discharge phase communicates with an outlet. Rotary screw compressors of this kind are often provided with valves for regulating the built-in volume ratio for the capacity of the compressor. When continued regulation is required, slide valves are often used, however, with other regulation needs, it is sufficient to use bypass valves. Such bypass valves are mounted in the barrel wall the compressor or may be mounted in one of the end walls and in this regard, normally in the high pressure end wall. A bypass valve arrangement of this general type is shown in U.S. Pat. No. 4,453,900 issued Jun. 12, 1984. However, the opening of the bypass valve is directly dependent upon the compression spring as well as the internal pressure of the compressor. The opening and closing of this type of valve is unreliable due to friction, corrosion and other environmental factors which often derogate the positioning this type of bypass valve. Further, while the face of the valve element takes on the approximate shape of the barrel, the valve element is separately formed by casting or other process within predetermined tolerances. In order to economically manufacture such valve elements, the tolerances must be some what relaxed which may result in the leakage of pressurized fluid between compression chambers thereby degrading the efficiency of the compressor.
These compressors may be controlled by electronic circuits, such as those disclosed in U.S. Pat. Nos. 4,336,001 and 4,227,862 to Andrew et al., which show electronically controlled startup and shutdown routines and control of a bypass slide valve to vary compressor output to maintain pressure at a selected setpoint.
U.S. Pat. Nos. 4,519,748, 4,516,914, and 4,548,549 to Murphy et al. and U.S. Pat. No. 4,609,329 to Pillis et al. show additional electronic control systems for compressors. However, the operating modalities of these systems are primarily designed for refrigerant compression.
U.S. Pat. No. 4,502,842 to Currier et al., assigned to Colt Industries Operating Corp., shows a single electronic control system which can be connected to control a plurality of variably sized compressors. The system gathers data on the operating characteristics of the controlled compressors during a calibration phase and then uses this information to load and unload the compressors during operation, maintaining a preset pressure which can be programmed to vary with time. High and low pressure set points are programmed into the electronic control system and the compressors are selective loaded and unloaded in a predetermined sequence. However, centralized master controllers of this type represent a single point of failure for the entire pressurized air system, and are lacking in versatility since they provide only a limited selection of control modalities.
U.S. Pat. No. 4,335,582 to Shaw et al. shows a system for unloading a helical screw compressor in a refrigeration system. A slide valve is connected so that upon compressor shutdown, the slide valve is automatically driven to a full unload position. This operation is accomplished with air pressure rather than with an electronic control system.
None of the electronic control systems described above provide a complete and versatile solution to the problems experienced when operating one or more compressors in a variety of plant installations with a variety of air storage capacities. In fact, the networking capabilities and choice of operating modes in prior art systems of the type described above, and the ability of the systems to dynamically adjust to changing conditions, are quite limited.
Thus, the inventors have found that there is a need for an improved and more versatile electronic control system for rotary screw compressor installations that will provide more efficient, safe, and reliable compressor operation.
Therefore, it is a general object of the present invention to provide a novel and improved electronic control system for controlling a compressor.
Another general object of the invention is to provide a novel and improved electronic control system for coordinating the operation of a plurality of electronic compressor control units.
A further general object of the invention to provide novel and improved methods for electronically controlling a compressor.
An additional general object of the invention is to provide novel and improved methods for interconnecting a plurality of electronic compressor control units to coordinate control of a plurality of compressors.
A more specific object of the present invention is to provide a novel and improved electronic control system for interactively controlling a plurality of rotary screw compressors in a peer-to-peer network where each compressor has a controller that communicates with the other controllers in the network and controls its associated compressor in accordance with predetermined network control algorithms.
Another object of the invention is to provide an electronic control system with a self adjusting control algorithm which automatically adjusts the operating points of compressor capacity control valves in response to changes in pressure setpoints.
Yet another object of the invention is to provide a method of dynamically adjusting pressure deadbands in a continuous run or auto/dual operation mode in response to changes in operator inputs, and in response to system characteristics sensed over time using a state machine algorithm.
A further object of the invention is to provide a versatile electronic compressor control system and method providing a plurality of operational mode choices, including a continuous run mode, an auto/dual operation mode, a pressure setpoint mode, and a networked multiple machine pressure setpoint mode.
It is also an object of the invention to provide electronic control systems for compressors which can be networked to create a virtual compressor array, with the individual electronic control systems providing coordinated peer-to-peer control of the compressor array for maximum operating efficiency in response to varying demand conditions.
Another object of the invention is to provide an electronic compressor control system with a manual operation mode which disables electronic control of the compressor system and operates the compressor based on a redundant mechanical and pressure control apparatus provided in the compressor system.
Yet another object of the invention is to provide an improved electronic control system for a compressor in which complete information describing the configuration and operating status of each compressor in a network is reported to each of the electronic control systems connected to the network.
An additional object of the invention is to provide a peer-to-peer network for electronic compressor control systems which configures itself automatically upon startup and will continue to operate despite the failure of any individual electronic control system forming a part of the network.
Another object of the invention is to provide a system and method for remote access via a communications link to an electronic compressor control system, permitting diagnosis, monitoring, control, and firmware updates without an on-site service call.
It is also an object of the invention to provide a system and method for remote access to a network of electronic compressor control systems, permitting monitoring, control, diagnosis, and firmware updates of any electronic control system in the network through a link to a single system in the network.
Another object of the invention is to provide an improved user interface for an electronic compressor control system including menu driven operation and a simplified, fail-safe control panel providing easy to understand operating status and fault specifications.
Yet another object of the invention is to provide an improved electronic compressor control system and method in which operating condition data is archived to facilitate diagnosis of compressor problems and to aid in fine tuning operating modes and setpoints to achieve peak operating efficiency of the compressor system.
Another object of the invention is to provide an improved electronically operated lift valve control system and method utilizing double acting lift valves to positively open and close bypass passages for varying the output capacity of the compressor.
A further object of the invention is to electronically detect unsafe operating conditions using an electronic control system for a compressor, and to prevent operation of the system when a failure is detected.
Another object of the invention is to electronically detect reverse rotation of a compressor motor using an electronic control system associated with the compressor, and to shut down the compressor and provide a warning when reverse rotation has been detected.
It is also an object of the invention to provide an electronic control system and method for a compressor system which allows testing of capacity control valve operation, including the inlet valve.
Another object of the invention is to provide an electronic control system and method for operating a compressor system which provides an orderly electronically controlled shutdown and blowdown of the compressor in response to an operator command.
Still another object of the invention is to provide an improved electronically controlled compressor system and method which prevents rapid cycling of a compressor inlet valve during periods of reduced demand by automatically switching between a cycling mode and a modulation mode of operation based on the settings of operator-adjustable control parameters.
These and other objects of the invention which will be apparent on reviewing the specification and microfiche appendix can be achieved using the improved electronic control system and methods disclosed herein.
In a preferred embodiment, an electronic control system dynamically varies the output capacity of a compressor by controlling plural valves associated with the compressor to provide pressurized air to a distribution system at an appropriate rate. The control system operates in any of three modes for standalone operation, including continuous run, auto/dual pressure band, and target pressure modes. In the first two modes, pressure bands are dynamically calculated based on load and unload values entered by an operator. These electronic control systems can also be connected in a peer-to-peer network to coordinate control of up to 16 compressors feeding the same distribution system, so as to maintain a desired target pressure in the system. A modem connected to the system supports remote diagnostics, monitoring, and control. Specialized startup, operating, and shutdown diagnostic algorithms prevent damage to the compressor and avert unsafe operating conditions.